In my program I need a very slow PWM signal where I can change the duty cycle, and since in the meanwhile I want to keep reading serial data I was planning to use the PWM function of the atmega.

I've been reading around how to do it http://www.electronicsblog.net/atmega8-pwm-controlfrequencypolarityduty-cycle-example-tutorial-with-program/http://www.nunoalves.com/classes/spring_2012_cpe355/cpe355-02-f.pdf

and so far I succeed in changing PWM duty cycle by changing OCR2 but I had no success in shifting down the frequency. I have an arduino ng with atmega8, the pwm signal is on pin 9 and below there's the code for changing the PWM timing options